Submarine carrier telegraphy



Oct. 29, 1929. A. M, CURTIS SUBMARINE CARRIER TELEGRAPHY Filed Feb. 2,1927 Patented Oct. 29, 1929 lUNITED STATES PATENT OFFICE AUSTEN M.CURTIS, EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY,INCORPORATED, F NEW YORK, N. Y., A CORPORATION 0F NEW 'YORK SUBMARINECARRIER TELEGRAPHY Application led February 2, 1927. Serial No. 165,282,

This invention relates to carrier telegraph systems and moreparticularly to systems employing a submarine cable.

The primary object of the invention is to improve the operation of lowfrequency carrier telegraph receiving systems.

There are technical difficulties involved in duplex transmission ofordinary code impulses over long loaded submarine cables.

Since duplex operation has many advantages it has been proposed toemploy carrier currents of a rat er igh frequency i. e., the range of150 to 400 cycles per second or considerably higher. Such frequenciesare spoken of as rather high in the sense that they are high for longsubmarine cable telegraphy. Viewed from the standpoint of carriercurrents they are low frequencies, especially s ince only a few cycleswill constitute a signal element.

2o Such a system has been found to necessitate the use of highlyselective receiving circuits in order to prevet the outgoing carrierWaves from affecting the receiver. Since the use of such frequencieswill permit the use of several channels, if the selectivity issufficiently good, the invention also relates to plural channelsubmarine cable operation, either one-way or duplex. Therefore inreading this specification it is to be kept in mind that the receivingcircuit referred to is especially adaptable for use in duplex or pluralchannel submarine cable telegraph operation. Consequently, a furtherobject of the invention is to improve the operation of duplex and pluralchannel submarine cable telegraph systems.

A preferred embodiment of the invention, specifically stated, resides inthe submarine cable receiving system herein disclosed for the receptionof carrier waves of relatively 4o" low frequenc but higher than the fre-"quency at which communication is to be effected, modulated fortransmission of code signals. It comprises a sharply tuned selectingcircuit having inductance and capacity elements, to select waves of acomparatively narrow band of frequencies. Circuits of this type do notpermit the carrier current to build up quickly and therefore distortionis introduced in the signals in a manner analogous to the effect of along cable on ordinary direct current sending and, as heretofore used,puts a limit to the speed of signaling. The distorted signals are thenpassed through an amplifier and a rectifier into a filter Where thehigher frequency carrier and harmonics are entirely suppressed. Therelatively lower frequency signals which pass through the filter retaintheir distorted wave shape and in order to give these signals a morenearly squaretopped form such as they had when originally transmitted, ashaping network is provided in the circuit connecting the filter with arecording device. A type preferred in this invention comprises anarrangement in which a path containing a variable inductance and avariable resistance in series is connected across the output terminalsof the filter and between this path and a terminal of the recording device is serially inserted a condenser shunted by a resistance followedby a serially arranged resistance.

The invention will be more particularly de- Ascribed in connection withthe accompanying drawing, wherein Fig. 1 is a circuit diagram of areceiving system embodying the invention; and Fig. 2 is a diagram of theform of signaling waves before and after the Waves pass through theshaping network at the receiving station.

In Fig. 1 modulated Waves of a plurality of frequencies are transmittedthrough several channels over submarine cable l. Circuit 2 represents asingle section highly selective selecting circuit which is adapted to besharply tuned to waves of one of these carrier frequencies. Thisresonant circuit is regarded as typical of any one of a number of highlyselective circuits of one or more sections adapted to transmit narrowranges of frequencies, and is connected to the input circuit of a vacuumtube amplifier 3. The cathode of this tube is connected to the anodethrough the usual plate, or B, battery 4 and the primary winding of atransformer 5. The secondary winding of the transformer is or connectedacross the receiving circuit which extends at one side through a cathodeand an anode of a rectifier 6 to a high frequency cut-off filter 7 andat the other side directly to the filter. The amplifier is used tomagni- 1 fv theniodulated waves selected by the resonant circuitbeforerectication, because the oscillations of the waves in the resonantcircuit may be too weak to operate the rectifier. It has been found in aseries of tests that if the resonant circuit is tuned sharply enough sothat the low frequency and high frequency channels ,are satisfactorilyseparated, the

high frequency dots run together at a speed of about ten words a minuteand therefore in order to avoid this condition and raise the speed ofsigna-ling, the carrier Wave is rectified. The rectified current is thenpassed through an integrating device such as the filter 7 wherein thecarrier and the harmonies are suppressed and the direct currentsignaling waves are permitted to continue on to a receiving instrument 8Which may be an oscillograph, siphon recorder, or any of the recordingor indicating types adapted for telegraph reception. If the directcurrent signaling waves were to be recorded on the receiving instrumentimmediately upon leaving the filter, the record Would show the signalsrounded off in a manner analogous to the signals received over a longcable with ordinary direct current sending, because the distortionintroduced by the resonant circuit is carried through the amplifier,rectifier and filter. This distortion is corrected by passing thesignaling current, after it leaves the filter, through a shaping networkconsisting of a variable inductance 9 and a variable resistance 10connected in series andarranged as a shunt path across the outputcircuit of the filter, and a shunted condenser 1l and a resistance l2arranged in series in one side of the output circuit and connectedbetween the shunt path and the receiving instrument.

In Fig. 2 A represents a graph of the signal Wave When it is recordedimmediately after passing through the filter and B represents the sameWave after it has passed through the shaping network and is recorded.Assuming, that the curves are plotted to the same scale it will be notedthe Waves in passing through the shaping network, under- -go aconsiderable reduction in amplitude, but this reduction is anticipatedan-d provided for in the amplifier.

This invention has been used satisfactorily in tests made over a 1500mile dummy loaded cable in Which the highest carrier frequency employedwas approximately 150 cycles, al-

though in cables of somewhat shorter lengths,

the carrier frequency may be as high as 400 cycles. The carrier currentwas modulated by direct current signals which effected a frequency rangein the combined current of about one-third of the frequency of thecarrier. It has also been tested and operated satisfactorily on anactual submarine cable about 2,000 miles long.

It is to be understood that selecting circuits other than a circuitcontaining single inductance and capacity elements may be used in placeof circuit 2, and thatvarious other modifications of the system hereinshown and described may be made without departing from the spirit andscope of the invention. Itis applicable also to considerably highercarrier frequencies than those herein mentioned.

l'Vhat is claimed is:

l. A low frequency carrier submarine telegraph system comprising ahighly selective receiving circuit for selecting a received modulatedcarrier current, means including an integrating device to separate thelow frequency signaling components from the carrier components of saidcurrent, and a network upon which said low frequency Waves are impressedto correct for the distorition introduced in the modulated carriercurrent by said selective circuit, said network including seriescapacity and shunt impedance.

2. A low frequency carrier submarine telegraph system comprising ahighly selective receiving circuit for selecting a received modulatedcarrier current, means including an integrating device to separate thelow frequency signaling components from the carrier components of saidcurrent, a low frequency translating device, a line for supplying saidlow frequency Waves to said translating device, and a. network uponwhich said low frequency Waves are impressed to correct for thedistortion of the modulated carrier current of the selective circuit,said network consisting of an inductance and a resistance in series witheach other and in shunt to said line and ca acity in series with theline.

l. A low frequency carrier submarine telegraph system comprising ahighlyselectiveV receiving circuit for selecting a received modulatedcarrier current, means including an integrating device to separate thelow frequency signaling components from the carrier components of saidcurrent, a low frequency translating device, a line for supplying said10W frequency Waves to said translating device, a network upon whichsaid low frequency Waves are impressed to correct for the distortion ofthe modulated carrier current of the selective circuit, said networkcomprising an inductance and a resistance in series With each other andin shunt to said line, a condenser in series With said line,`aresistance in shunt to said condenser and a second resistance in serieswith said line.

4. A carrier cable telegraph system comprising aline for transmitting aplurality of low frequency signal-modulated carrier currents, areceiving circuit for selecting one of said modulatedcurrents, meansincluding an integrating device for deriving the si al component fromsaid selected modulated current, and a network proportioned to attenuatethe lower frequencies of said signal component more than the higherfrequencies and to thereby correct for distoration introduced in saidselected modulated current by said receiving circuit, said networkincluding shunt inductance and series capacity and resistance.

5. A. carrier submarine telegraph system comprising a submarine cablefor transmitting a plurality of low frequenc signalmodulated carriercurrents, a hig ly selective receiving circuit for selecting one of saidmodulated currents, means including an integratin device for derivingthe signal component irom said modulated current, a low frequencytranslating device, a circuit for supplying said signal component tosaid translating device,a network between said integrating and saidtranslating devices proportioned to distort said signal component andcorrect for distortion of said selected modulated current, said networkcomprising an inductance and a resistance in series with each other andin shunt to the second mentioned circuit, a condenser in series with thesecond mentioned circuit, and a resistance in shunt to said condenser.

In witness whereoLI hereunto subscribe my name this 31st day of January,A. D.

AUSTEN M. CURTIS.

